Field of the Invention
The invention provides novel UV radiation absorbing compounds having at least one reactive hydrogen. The invention further provides a wide variety of formulations comprising a UV-absorbing compounds.
Description of Related Art
It is now generally accepted that ultraviolet (UV) radiation can be a serious health hazard. Even a limited exposure to solar radiation can cause short- and long-term skin damage, such as erythema, burns, wrinkles, lentigo (“liver spots”), skin cancers, keratotic lesions, and other cellular changes. There is a greater risk for developing such conditions for those who send prolonged time in the sun, such as for their occupation or during recreation.
UV radiation is just one portion of the electromagnetic spectrum with wavelengths from about 100 nm and about 400 nm, and is further divided into three subregions. UV-A radiation, from about 320 nm to about 400 nm, has the longest wavelength within the UV spectrum, and consequently is the least energetic. While UV-A rays can induce skin tanning, they are liable to induce adverse changes as well, especially in the case of sensitive skin or of skin which is continually exposed to solar radiation. In particular UV-A rays cause a loss of skin elasticity and the appearance of wrinkles, leading to premature skin aging. UV-B rays have shorter wavelengths, from about 290 nm to about 320 nm, and their higher energy can cause erythema and skin burns which may be harmful. The third subgroup, UV-C has the shortest wavelengths, from about 200 nm to about 290 nm, and the highest energy. The Earth's ozone layer effectively filters much UV-C radiation from reaching the ground. Nonetheless, UV-C rays can be generated from tanning bed devices.
In addition to harming the skin, UV radiation can injure the hair, resulting in color changes (especially for color-treated hair), embrittlement, and a loss in aesthetics (e.g., shine, manageability).
UV radiation damage is not limited to the skin and hair, as inanimate objects exposed to solar radiation can experience changes related to color, hardness, and structural integrity, which can contribute to aesthetical and functional deterioration. Thus, there is the very real and demanding need for compositions that protect the skin, hair, and objects from UV rays, especially UV-A and UV-B radiation. Of special interest are compositions that provide broad UV-spectrum protection from both UV-A and UV-B radiation.
Broadly speaking, para-aminobenzoic acid (PABA) exhibits a common trait shared with many UV absorbers/filters. The molecule possesses both electron withdrawing and electron accepting groups, providing resonance delocalization that coincides with the absorbed energy of UV radiation:

However, PABA is a highly polar molecule, making it water soluble, and giving it low persistence, meaning that it is not highly retained on the skin after swimming or perspiring. In addition, due to extensive intermolecular bonding, PABA exists as a solid, which may further complicate its formulation. Thus, there exists the need to improve the persistence of UV absorbers, especially those that are water-soluble, and to provide formulation flexibility.
UV absorbers may exhibit photolability, in which the absorbed energy causes photodegradation and/or photoreactivity, and thus reduce its efficacy. Such photolability may result from irreversible isomerisms (i.e., keto-enol tautomerism and cis-trans isomerism), photocleavage, and/or photoaddition, and may be formulation sensitive, (e.g., blends of avobenzone and octinoxate). Examples of photolabile UV absorber include, without limitation: avobenzone, PABA derivatives, cinnamates, and dibenzoyl methane derivatives, all of which degrades over time, and reduce UV protection. Hence, there exists a need to stabilize UV absorbers from photodegradative effects.
Additionally, there exists the need to enhance the efficacy of UV absorbers without increasing their content in the formula, since a maximum addition level frequently is regulated. This efficacy need is especially important for avobenzone, a highly effective UV-A absorber. Avobenzone is subject to keto-enol isomerization due to formulation dependencies (e.g., solvent, other UV absorbers):

The enol tautomer (left) has its maximum absorbance at 357 nm, which identifies it as a UV-A absorber. Unfortunately, avobenzone is subject to bimolecular reactions (viz., via cleavage mechanisms) that alter the molecule's structure and decrease its effectiveness as an UV absorber. Hence, an effective method is needed for stabilizing labile chromophores like avobenzone in order to enhance their efficacy without increasing their addition level.
Methods for stabilizing chromophores, and in particular UV absorbers, are known in the prior art. For example, Japanese patent 1971/26,860 describes UV stabilizers having amino, hydroxyl, or isocyanate groups attached to crosslinked polymers, being crosslinked glycidyl methacrylate-divinylbenzene copolymers or crosslinked styrene-maleic anhydride-divinylbenzene copolymers.
Related to the invention are the following references: European Patents 303,283 and 1,972,323; U.S. Pat. Nos. 3,001,970; 3,878,229; 3,879,443; 4,256,664; 4,489,057; 4,680,144; 4,868,246; 5,071,898; 5,344,992; 5,427,773; 5,451,394; 5,741,924; 5,808,165; 6,410,795; 7,045,139; and 7,147,866; U.S. Patent Application 2004/0208837; and WO 2007/143209.
Further related are articles by Kita, et al. published in Angewandte Chemie International Edition, volume 51 (2012), issue 23, page 572; by Song et al. published in Journal of American Chemical Society, volume 111 (1989), issue 22, page 847; by Bender et al., published in Tetrahedron, volume 60 (2004), page 7277;
Also related is a sales specification for 1,3-propanedione, 1-(4-hydroxyphenyl)-3-(4-methylphenyl) (CAS No. 52046-72-7) from
There is still a need to develop compounds having good UV radiation absorption properties and having one or more reactive hydrogen(s) in the molecule amenable for further functionalization. The invention provides novel UV radiation absorbing compounds having at least one reactive hydrogen atom.